ELECTRODYNAMIC DRIVE

Abstract

The invention relates to a highly dynamic electromagnetic drive in the manner of a Thomson coil with soft-magnetic frame, comprising a first excitation coil (30) whose winding height is greater than its length, which hence is flat; a soft-magnetic frame (10) in which the first excitation coil (30) is arranged and against which it abuts, and which in in the manner of a pot magnet constitutes an open magnetic circuit which includes an outer region (11), a bottom (12) and an inner region (13), and which is open on its end face, wherein the first excitation coil at least partly encloses the inner part (13) of the frame; a short circuit armature (40) preferably formed hollow cylindrical at least on its side facing the first excitation coil (30), which is movably mounted along an axis and which in its stroke starting position dips into the end-face opening of the frame (10) and thereby at least partly encloses the inner part of the frame (13), wherein the frame (10) entirely or predominantly is formed of a soft-magnetic composite material or one or more sheet stacks, which has a saturation flux density of at least 1.5 T and an effective specific electrical conductivity of not more than 10.sup.6 S/m, and the first excitation coil (30) and/or the frame (10) include at least one means for strain relief, in particular in the form of an enclosure in order to at least partly absorb at least the radial forces occurring on the first excitation coil (30) during an actuating operation vertically to the direction of movement, and wherein the Lorentz force acting on the short circuit armature is used to perform work.

Claims

1. An electrodynamic drive comprising: a first excitation coil, a soft-magnetic frame, and a short circuit armature mounted movably along an axis, wherein the frame has a saturation flux density of at least 1.0 T and an effective specific electrical conductivity of not more than 10.sup.6 S/m.

2. The electrodynamic drive according to claim 1, wherein the first excitation coil and/or the frame include at least one means for strain relief, and/or wherein the excitation coil has a winding height which is greater than its length, which hence is flat, and/or wherein the excitation coil is arranged in the soft-magnetic frame and abuts against the same.

3. The electrodynamic drive according to claim 1, wherein the frame represents an open magnetic circuit which includes an outer region, a bottom and an inner region, and which has an end-face opening, wherein the first excitation coil at least partly encloses the inner part of the frame, and wherein the short circuit armature in its stroke starting position dips into the end-face opening of the frame and thereby at least partly encloses the inner part of the frame.

4. The electrodynamic drive according to claim 1, wherein the soft-magnetic frame entirely or predominantly is formed of a soft-magnetic composite material and/or one or more sheet stacks.

5. The electrodynamic drive according to claims, claim 3, wherein the short circuit armature dips into a space between the outer and inner region of the frame which has the shape of cylinder jacket, wherein its longitudinal axis corresponds to a direction of movement of the drive and/or a winding axis of the coil(s).

6. The electrodynamic drive according to claim 4, wherein the frame made of a soft-magnetic composite material is composed of several parts and/or segments which are adhesively bonded or potted to each other.

7. The electrodynamic drive according to claim 1, wherein the short circuit armature of the drive wholly or partly is formed of a non-magnetic material and/or wherein the short circuit armature on the bottom side, i.e. in the stroke starting position, has a ring of electrically well conducting material on the side of the short circuit armature facing the first excitation coil.

8. (canceled)

9. The electrodynamic drive according to claim 7, wherein the ring entirely or predominantly has an expansion in direction of movement of at least 1=sqrt (t*rho/pi*), wherein t is the half-value width of the current in the excitation coil during a proper actuating operation, rho is the specific electrical resistance of the ring, pi is the circular ratio and is the magnetic field constant.

10. (canceled)

11. The electrodynamic drive according to claim 1, wherein it at least partly is operated by means of a capacitor discharge.

12. The electrodynamic drive according to claim 11, wherein the capacitor discharge is accomplished by switching one or more semiconductor switches.

13. The electrodynamic drive according to claim 12, wherein the semiconductor switch is protected from being damaged during the operation by a saturating inductance, in that the saturating inductance is dimensioned to sufficiently limit the initial rate of current rise dl/dt.

14. The electrodynamic drive according to claim 1, wherein it comprises a lifting magnet or is operated on such lifting magnet, wherein an armature of the lifting magnet transmits an impulse to the short circuit armature during an actuating operation by means of a chiefly elastic impact in order to accelerate the same, and wherein a capacitor discharge is carried out in synchronism with the elastic impact via the first excitation coil.

15-19. (canceled)

20. The electrodynamic drive according to claim 2, wherein the first excitation coil is potted and additionally strain-relieved against the (Lorentz) forces acting during an actuating operation by a fiber reinforcement, and/or wherein the strain relief is effected in a cylindrical enclosure of the coil by means of a fiber-reinforced composite material radially within the outer region of the frame.

21.-35. (canceled)

36. An electric hammer driven by an electrodynamic drive according to claim 1.

37. An impact drilling machine comprising an impact mechanism driven by an electrodynamic drive according to claim 1 or is formed by such drive.

38. An arc fault protection device comprising an electrodynamic drive according to claim 1.

39. The arc fault protection device according to claim 38, which furthermore comprises at least one electric insulating plate and at least one metallically conducting bolt, wherein the electrodynamic drive(s) is/are actuated such that the detection of an accidental arc by external means leads to the fact that the bolt(s) is/are accelerated by the electrodynamic drive(s) in order to break through the insulating plate and accomplish a single- or multi-phase short circuit, so as to withdraw electric power from the accidental arc.

40. An electric switch comprising an electrodynamic drive according to claim 1, which is used to open the electric switch.

41. A short-circuit current limiter comprising an electric switch according to claim 40, wherein as a result of the detection of a short circuit by external means the electrodynamic drive is actuated to open the switch, and that one or more inductances and/or a fuse is/are electrically connected in parallel with the electric switch.

42. A hybrid switch for separating a d.c. circuit comprising a switch according to claim 40, wherein it includes two parallel current paths, wherein a first current path can be interrupted by means of a first semiconductor switch to the effect that the current to be switched off chiefly commutes to the second current path which includes a second semiconductor switch, wherein the first semiconductor switch has a lower breaking capacity and a smaller series resistance than the second semiconductor switch, and wherein the switch is connected in series with the first semiconductor switch and in parallel with the second semiconductor switch.

Description

[0102] The present invention will now be explained in detail with reference to exemplary embodiments and drawings.

[0103] In the drawings:

[0104] FIG. 1 shows a longitudinal section through a first exemplary embodiment of a drive according to the invention,

[0105] FIG. 2 shows a detail view of a second exemplary embodiment of a drive according to the invention in a longitudinal section, wherein merely one half of the rotationally symmetrical construction is shown,

[0106] FIG. 3 shows several axial sections through segments of which the soft-magnetic frame is constructed in the exemplary embodiment shown in FIG. 1,

[0107] FIGS. 4a) to d) show another exemplary embodiment of a drive according to the invention with a resetting device, and

[0108] FIG. 5 shows an exemplary embodiment of a nail setting device according to the invention.

[0109] The following explanations serve to provide a better understanding of the invention, exclusively are to be regarded as an example and by no means are to be understood in a limiting sense.

[0110] In contrast to the above-mentioned concrete application of ABB, the frame (10) formed as a flux concentrator in the exemplary embodiment is formed of a soft-magnetic composite material (hereinafter: SMC for soft-magnetic composite) and/or of one or more soft-magnetic sheet stacks, which has a saturation flux density of at least 1.5 T and an effective specific electrical conductivity of not more than 10.sup.6 S/m. Preferably, the frame is formed of an SMC with a specific conductivity <10.sup.4 S/m, a saturation flux density B.sub.s1.9 T, and a maximum relative permeability .sub.r50. Furthermore, with regard to strength requirements the frame material(s) should be selected to have a high yield point. SMCs well-suited for the realization of the invention are known and available under the brand name Somaloy.

[0111] So far, SMCs do not reach the high saturation flux densities of the known magnetic iron-cobalt alloys (e.g. Vacoflux). In view of the high dynamic aimed at by the invention and for which the invention is intended, this fact in most individual cases however is less important by far than the effective attenuation of eddy currents in SMCs.

[0112] With the known soft-magnetic alloys (as solid materials), the properties desired according to the invention, such as dynamic and efficiency, cannot be achieved sufficiently.

[0113] Another essential aspect of the invention consists in a strain relief of the drive coil(s) and/or of the frame, as the properties desired according to the invention can be achieved only at very high magnetic pressures, which leads to a strong structural strain on the drive in each actuating operation. Beside enclosures (20) made of so-called Maraging steels, for example, in particular fiber composites can also be taken into consideration for a strain relief of the frame (10). For a strain relief of the coil (30) it is possible to pot high-strength fibers or textiles with or wind the same around the electric conductor(s) of the coil. Beside its tensile strength, the fiber material preferably is selected to have a higher tensile modulus than the electric conductor itself. Finally, the coil can be potted or overmolded, wherein the potting compound preferably is selected to on the one hand have a rather high inherent strength, a high yield point, and a high tensile modulusfor a polymer , and on the other hand to adhere to the electric conductor or to its paint surface as well as to the fiber material itself as firmly as possible. In case the drive is operated under conditions which lead to a significant thermal load of the coil, the potting compound also should be selected to have a high thermal conductivity; for this purpose, the potting compound itself can be filled correspondingly, for example with AN as filler.

[0114] The coil possibly can also be equipped with a cooling device, in particular with an active or passive liquid cooling, and/or a firm thermal connection of the coil to the soft-magnetic frame can be provided, which in turn can itself thermally be connected with a heat sink.

[0115] Finally, the invention will be explained with reference to a concrete example. FIGS. 1 and 2 show longitudinal sections of a first and a second exemplary embodiment of the drive with soft-magnetic frame (10) rotationally symmetrical about the axis (1), which is similar in shape to the frame of known pot magnets, with rounded lower edge, a strain-relieving enclosure of Maraging steel (20), a first excitation coil (30) directly or indirectly abutting against the frame (10), which is formed for example of fiber-reinforced flat wire and which is potted, wherein to control the skin effect each individual winding can be formed in the manner of a strand of several thin (flat) wires connected in parallel, and of the short circuit armature (40) which is made of a high-strength (curable) aluminum alloy (e.g. 7068), and in which on the side facing the coil an electrically excellently conducting ring (41) of (here e.g.) pure Cu is embedded.

[0116] Alternatively, it is possible to cohesively or positively connect a ring (41) (of Cu or Al or a Cu alloy or Al alloy with a strength greatly increased as compared to the pure metals, but with a rather good electrical conductivity), which for example has the same inner and outer radius as the remaining short circuit armature (40), with said short circuit armature (40) on its side facing the first excitation coil (30).

[0117] The compliance with all strength requirements in the construction of a concrete drive preferably is to be determined for the case of application with the aid of computer simulations (FEM).

[0118] In FIG. 1, an enclosure (20) in the form of a cylinder jacket is used as strain relief which surrounds the circumference of the frame (10) along its entire axial length. In FIG. 2, the enclosure (20) on the other hand has a bottom region in addition to the cylinder jacket.

[0119] On its outer circumference the short circuit armature has a plain bearing (42) with which the short circuit armature is axially shiftably mounted in a housing (50) of the drive. The short circuit armature (40) is connected with a piston (45) extending in axial direction, which serves the transmission of the forces produced by the short circuit armature. Proceeding from the short circuit armature, the piston extends through the interior of the housing and extends through a piston guide (49). Preferably, the piston (45) also is slidingly mounted.

[0120] There is preferably used a device or design which on return of the drive safely prevents (firm) setting of the short circuit armature (40) onto the first excitation coil (30) and hence avoids a possible damage of the coil.

[0121] The housing can serve as a shield for the drive in order to fulfill corresponding EMC criteria. Preferably, the housing therefore is fabricated of aluminum and/or an aluminum alloy.

[0122] In particular, curable aluminum alloys such as the alloy 7068 can be used in the cured condition, as they combine a high electrical conductivity with a high mechanical strength and sufficient corrosion resistance.

[0123] Furthermore, as a shield the drive can include apreferably thinouter enclosure of highly permeable soft-magnetic material (e.g. -metal) which also should have a high saturation polarization. What can be considered here in particular are foils, clearly superior to -metal, of soft-magnetic metallic glasses or nanocrystalline materials with saturation flux densities >1 T (and above all >1.2 T).

[0124] In FIG. 1 a surface (43) of the piston (10) or of the short circuit armature (40) facing the frame (10) therefor is designed as a stop by which the position of the short circuit armature in the stroke starting position is defined. The stop (43) can cooperate with the frame (10).

[0125] Preferably, the stop (43) however cooperates with an adjusting element by which the distance of the bottom-side end of the short circuit armature (40) or of the ring (41) to the excitation coil (30) can be adjusted in the stroke starting position. For example, a screw can be guided through the bore (14) in the frame (10) and serve as an adjustable counter-stop. It can thereby be prevented that the bottom-side end of the short circuit armature (40) or the ring (41) will damage the excitation coil (30) when it is returned into the stroke starting position.

[0126] FIG. 3 shows that the frame (10) can be composed of a plurality of parts (in the outer region of the frame of circular segments); in operation, this provides for a certain movement of the parts against each other, whereby a damage of the comparatively brittle SMC can be avoided. The frame parts likewise are potted or adhesively bonded to each other if possible, wherein a solid elastomer adhering well with high yield point, which is chemically compatible with the SMC, preferably should be selected as potting compound or adhesive.

[0127] The electric leads (52) to the first excitation coil (30), which are schematically shown in FIG. 1, should be realized such that the usable magnetic cross-section of the frame is impaired as little as possible by these inevitable leads. For operating the drive, a capacitor or a capacitor bank (58) can be discharged via the excitation coil (30) by means of a switch (56), in particular a thyristor. Furthermore, a free-wheeling diode is provided between the connections (59) of the capacitor or the capacitor bank. In particular when foil capacitors and/or film capacitors are used, the same can possibly also be omitted.

[0128] A controller (55) actuates the switch (56) and via a switching converter (54) furthermore performs charging of the capacitor or the capacitor bank.

[0129] The switch (56) preferably is a semiconductor switch, in particular a thyristor.

[0130] To satisfy the weight requirements, the highest demands also are placed on the switching converter. Preferably, the same includes semiconductor switches, in particular semiconductor switches with large band gap (e.g. SiC MOSFETs) and high-quality core material (above all cores of soft-magnetic metallic glasses and/or nanocrystalline alloys with discrete air gap).

[0131] As the self-induction of the coil, which anyway is low in view of the usually very small number of turns, is additionally shorted by the short circuit armature, the initial inductance of the arrangement is extremely low, which provides for the enormous dynamic in the first place. To protect the thyristor from too high a rate of current rise dl/dt, it may be recommendable to introduce a saturating inductance (so-called saturable reactor), for example by guiding a lead to the drive through a saturating highly permeable toroidal core (magnetic switch protection). Otherwise, the impedances of all components must be taken into account in the design of the outer wiring of the drive according to the invention. The number of turns of the excitation coil is to be adjusted both to the impedance of the voltage source and to the mechanical load, wherein the mechanical load for example is formed by the mass of the short circuit armature and of further parts possibly connected therewith, such as the piston. At a given constant capacity and number of turns, the electric efficiency of a drive according to the invention has a maximum at a particular mass to be accelerated and a mechanical load connected therewith. In many cases, the drive geometry disclosed in the Figures is suitable to directly design a highly dynamic drive for an application in this respect, without having to make an optimization of the same. In general, the drive operates in that the excitation coil (30) first of all repels the short circuit armature (40), wherein the associated force constants rapidly decrease with increasing distance, i.e. At given signals the repelling Lorentz force is the greater the smaller the distance between excitation coil (30) and short circuit armature (40). Accordingly, in the stroke starting position the excitation coil (30) and the short circuit armature (40) must be arranged as close as possible to each other.

[0132] When electrolytic capacitors are used as capacitors, intense heating of the capacitor can occur during the actuating operation due to the relatively high internal resistance. To remedy this problem it can be provided to switch off the electrolytic capacitors still during the actuating operation. This preferably is accomplished by blocking the semiconductor switch or by a free-wheeling possibility, in particular in the form of a free-wheeling diode.

[0133] The ohmic/real internal resistance of the electrolytic capacitor approximately corresponds to that of the coil. It preferably is provided to interrupt the discharge of the electrolytic capacitor after reaching the current maximum, while the electrolytic capacitor still is partly charged and a large part of the electrostatic energy from the electrolytic capacitor has been converted into magnetic field energy in the drive section.

[0134] The current linked with the magnetic field furthermore can flow over a rather low-impedance free-wheeling diode or another low-resistance free-wheeling device, which preferably has a lower effective loss resistance than the electrolytic capacitor itself. In this way, magnetic field energy is not unnecessarily converted into heat in the electrolytic capacitor, for example in its electrolytes.

[0135] Conventional thyristors cannot be switched off directly. Alternatively, GTOs, IGBTs, IGCTs, MCTs can be used, which can be switched off, but also incur comparatively high costs. What also is possible, however, is a brief reversal of the current direction in the thyristor (SCR1) by means of an in particular comparatively small second thyristor (auxiliary valve) and a (small) throttle, by at the same time switching off or changing the polarity of the current into the gate of SCR1.

[0136] Preferably, however, foil capacitors and/or film capacitors are used, which due to the low internal resistance do not require such switching off.

[0137] Foil and/or film capacitors always still have a lower energy density than it can be achieved with electrolytic capacitors, but foil and/or film capacitors can have an extraordinarily low electric series resistance (ESR). This low electric series resistance can considerably increase the efficiency.

[0138] Another advantage of foil and film capacitors is to be seen in that they are bipolar. They can bear to be reversed in polarity, so that a free-wheeling diode possibly can be omitted, which due to the related saving in weight is helpful in particular in the case of a hand-held device.

[0139] A combination of electrolytic capacitors and foil/film capacitors connected in parallel likewise is possible.

[0140] In the foil/film capacitors one balance must be made: Energy density vs. ESR. Here, the optimum (weight/efficiencydepending on the case of application) is to be determined numerically.

[0141] The drive still includes a device (80) for returning the piston (45) and/or the short circuit armature (40), which in FIG. 1 merely is shown in abstract form as a box, and will now be explained again by means of an exemplary embodiment with reference to FIGS. 4a to 4d. FIGS. 4c and 4d show the resetting device in a sectional view along the axis of movement of the drive in the two end positions.

[0142] The piston return can be effected for example by means of a soft-magnetic element (120) having a spatial extension for example along the direction of movement of the piston by at least one stroke length, which preferably is designed rod-shaped, for example a rod-shaped sheet stack or a soft-magnetic rod with slots. The soft-magnetic element (120) is connected with the piston, preferably rigidly connected, and/or forms the rear end of the piston. The soft-magnetic element preferably extends through an axial opening (14) through the frame and for example is arranged behind the bottom surface of the drive.

[0143] In line with the soft-magnetic element an arrangement (100) of permanent magnets (PM) exists, which form a magnetic circuit that is increasingly closed on return of the piston, in that the soft-magnetic element (120) increasingly moves into the arrangement.

[0144] The flux of the permanent magnets entirely or predominantly is guided into the soft-magnetic part vertically to the direction of movement. The permanent magnets can be configured in the manner of a so-called Halbach array in order to reduce the otherwise necessary back iron and hence save weight and nevertheless provide for a minimum stray field.

[0145] In FIGS. 4a and 4b two different aspects of such arrangements are shown, wherein the arrows indicate the direction of the polarization of the permanent-magnetic elements and/or regions. These are arrangements each in the form of a Halbach array.

[0146] With a Halbach array, in particular according to FIG. 4b, it is possible for example to guide the flux generated by the permanent magnets largely transversely through the movable soft-magnetic element (120): Along the direction of movement in a horizontally operated drive the field lines thus for example enter into the iron from below and exit from the iron at the top. Lateral movements of the iron (along the field lines, i.e. orthogonally to the direction of movement) then only lead to a minor change of the magnetic field energy, which is why such an arrangement is almost completely free from magnetic transverse forces, which otherwise might load e.g. bearings, for example a plain bearing guiding the soft-magnetic element.

[0147] Within the arrangement of permanent magnets a plain bearing (110) is provided for the soft-magnetic element. The arrangement of permanent magnets preferably annularly surrounds the soft-magnetic element and/or the plain bearing and/or has the shape of a hollow cylinder. FIG. 5 now shows an exemplary embodiment of a nail setting device according to the invention with a drive according to the invention, as it is shown in detail in FIGS. 1 and/or 4. With regard to the electrodynamic drive reference therefore is made to the above representation.

[0148] Beside the components of the drive, i.e. the first excitation coil (30), the soft-magnetic frame (10), the short circuit armature (40) movably mounted along the axis (1) and the strain relief (20), the hand-held nail setting device furthermore comprises at least one capacitor (58), at least one electrochemical energy storage device (53), in particular in the form of an accumulator, a switching converter (54), a switch (56), a piston (45), and a likewise only schematically illustrated resetting device (80) for the short circuit armature (40) and the piston (45). For setting a nail (70) the capacitor (58) first is charged with electric energy from the electrochemical energy storage device (53) by means of the switching converter (54), whereupon the switch (56) is closed in order to accomplish a discharge of the capacitor (58) via the excitation coil (30), whereupon the short circuit armature (40) and the piston (45) are accelerated out of their stroke starting positions, and the piston (45) is used to drive in the nail (70), and whereafter the resetting device (80) is used to return the piston (45) and the short circuit armature (40) into the stroke starting positions.

[0149] Driving in the nail is effected by the tip of the piston (45) striking on a nail (70) which for example is provided in a magazine (68) arranged on the front side of the nail setting device.

[0150] The nail setting operation is triggered by actuating the trigger switch (52), e.g. by pressing a key (63). The controller (55), however, only allows triggering of a nail setting operation when the tip of the nail setting device has made contact, which is detected via the contact switch (66). The controller (55) queries the contact switch (66) and the trigger switch (52) and actuates the switching converter (54) and the switching converter (56).

[0151] The nail setting device (60) furthermore includes a damper (65) which is suitable to absorb the kinetic energy of the piston and possibly prevent a destruction of the device also for the case that the nail can be set without a significant expenditure of work. In the present case, the damper is provided at the outlet of the housing (50).

[0152] Beside the drive the housing (61) of the nail setting device furthermore also surrounds the capacitors (58) which in the present case are arranged in the housing in axial direction behind the drive.

[0153] The housing can serve as outer housing of the capacitors which therefore do not require their own enclosure. In the region of the capacitors (58) the housing preferably is fabricated of metal in order to ensure a high thermal conductivity and hence a good cooling of the capacitors.

[0154] The housing of the nail setting device comprises a handle region (62) on which the key (63) is arranged. The electrochemical energy storage device (53), in particular in the form of an accumulator, preferably is arranged in a separate housing part (64) which is releasably connectable with the remaining housing in order to be able to change the electrochemical energy storage device.